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// @file mutex.h
/* Copyright 2009 10gen Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <map>
#include <set>
#include "../heapcheck.h"
namespace mongo {
class mutex;
inline boost::xtime incxtimemillis( long long s ) {
boost::xtime xt;
boost::xtime_get(&xt, boost::TIME_UTC);
xt.sec += (int)( s / 1000 );
xt.nsec += (int)(( s % 1000 ) * 1000000);
if ( xt.nsec >= 1000000000 ) {
xt.nsec -= 1000000000;
xt.sec++;
}
return xt;
}
/** only used on _DEBUG builds.
MutexDebugger checks that we always acquire locks for multiple mutexes in a consistant (acyclic) order.
If we were inconsistent we could deadlock.
*/
class MutexDebugger {
typedef const char * mid; // mid = mutex ID
typedef map<mid,int> Preceeding;
map< mid, int > maxNest;
boost::thread_specific_ptr< Preceeding > us;
map< mid, set<mid> > followers;
boost::mutex &x;
unsigned magic;
void aBreakPoint() { } // for debugging
public:
// set these to create an assert that
// b must never be locked before a
// so
// a.lock(); b.lock(); is fine
// b.lock(); alone is fine too
// only checked on _DEBUG builds.
string a,b;
/** outputs some diagnostic info on mutexes (on _DEBUG builds) */
void programEnding();
MutexDebugger();
void entering(mid m) {
if( this == 0 ) return;
assert( magic == 0x12345678 );
Preceeding *_preceeding = us.get();
if( _preceeding == 0 )
us.reset( _preceeding = new Preceeding() );
Preceeding &preceeding = *_preceeding;
if( a == m ) {
aBreakPoint();
if( preceeding[b.c_str()] ) {
cout << "****** MutexDebugger error! warning " << b << " was locked before " << a << endl;
assert(false);
}
}
preceeding[m]++;
if( preceeding[m] > 1 ) {
// recursive re-locking.
if( preceeding[m] > maxNest[m] )
maxNest[m] = preceeding[m];
return;
}
bool failed = false;
string err;
{
boost::mutex::scoped_lock lk(x);
followers[m];
for( Preceeding::iterator i = preceeding.begin(); i != preceeding.end(); i++ ) {
if( m != i->first && i->second > 0 ) {
followers[i->first].insert(m);
if( followers[m].count(i->first) != 0 ) {
failed = true;
stringstream ss;
mid bad = i->first;
ss << "mutex problem" <<
"\n when locking " << m <<
"\n " << bad << " was already locked and should not be."
"\n set a and b above to debug.\n";
stringstream q;
for( Preceeding::iterator i = preceeding.begin(); i != preceeding.end(); i++ ) {
if( i->first != m && i->first != bad && i->second > 0 )
q << " " << i->first << '\n';
}
string also = q.str();
if( !also.empty() )
ss << "also locked before " << m << " in this thread (no particular order):\n" << also;
err = ss.str();
break;
}
}
}
}
if( failed ) {
cout << err << endl;
assert( 0 );
}
}
void leaving(mid m) {
if( this == 0 ) return; // still in startup pre-main()
Preceeding& preceeding = *us.get();
preceeding[m]--;
if( preceeding[m] < 0 ) {
cout << "ERROR: lock count for " << m << " is " << preceeding[m] << endl;
assert( preceeding[m] >= 0 );
}
}
};
extern MutexDebugger &mutexDebugger;
// If you create a local static instance of this class, that instance will be destroyed
// before all global static objects are destroyed, so _destroyingStatics will be set
// to true before the global static variables are destroyed.
class StaticObserver : boost::noncopyable {
public:
static bool _destroyingStatics;
~StaticObserver() { _destroyingStatics = true; }
};
/** On pthread systems, it is an error to destroy a mutex while held. Static global
* mutexes may be held upon shutdown in our implementation, and this way we avoid
* destroying them.
* NOT recursive.
*/
class mutex : boost::noncopyable {
public:
#if defined(_DEBUG)
const char * const _name;
#endif
#if defined(_DEBUG)
mutex(const char *name)
: _name(name)
#else
mutex(const char *)
#endif
{
_m = new boost::timed_mutex();
IGNORE_OBJECT( _m ); // Turn-off heap checking on _m
}
~mutex() {
if( !StaticObserver::_destroyingStatics ) {
UNIGNORE_OBJECT( _m );
delete _m;
}
}
class try_lock : boost::noncopyable {
public:
try_lock( mongo::mutex &m , int millis = 0 )
: _l( m.boost() , incxtimemillis( millis ) ) ,
#if BOOST_VERSION >= 103500
ok( _l.owns_lock() )
#else
ok( _l.locked() )
#endif
{
}
~try_lock() {
}
private:
boost::timed_mutex::scoped_timed_lock _l;
public:
const bool ok;
};
class scoped_lock : boost::noncopyable {
#if defined(_DEBUG)
mongo::mutex *mut;
#endif
public:
scoped_lock( mongo::mutex &m ) : _l( m.boost() ) {
#if defined(_DEBUG)
mut = &m;
mutexDebugger.entering(mut->_name);
#endif
}
~scoped_lock() {
#if defined(_DEBUG)
mutexDebugger.leaving(mut->_name);
#endif
}
boost::timed_mutex::scoped_lock &boost() { return _l; }
private:
boost::timed_mutex::scoped_lock _l;
};
private:
boost::timed_mutex &boost() { return *_m; }
boost::timed_mutex *_m;
};
typedef mutex::scoped_lock scoped_lock;
typedef boost::recursive_mutex::scoped_lock recursive_scoped_lock;
}
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